Nitrogen Fertilizer Needs of First-Year Corn Grown after Alfalfa.

Crop response to N fertilizer can vary due to climate, geography, soils, pest problems, field history, and other factors. Preliminary studies in Cache County suggested that we may be able to update USU N fertilizer recommendations for first-year corn grown after alfalfa, resulting in substantially less fertilizer being applied and significant cost savings to growers. The objective of this project was to test the N fertilizer response of first year corn after alfalfa at locations across the state to ensure the validity and promote adoption of the new N fertilization recommendations.  Studies were conducted at farms in 6 Utah counties (Box Elder, Cache, Davis, Sevier, Uintah, and Weber) during the 2014 growing season.  Growers in each county were contacted by the county Extension agent and agreed to host a trial on their farms.  Fields in which the experiments were located were all in alfalfa production in 2013 and were planted to corn in 2014.  Four rates of N fertilizer (0, 50, 100, and 200 lbs N/acre) were applied broadcast as NH₄NO₃ to plots measuring four rows (10 ft) wide by 40 ft long.  Treatments were arranged in a randomized complete block and replicated four times. Fields were sampled for soil fertility, stand count, corn yield and corn quality as described in the proposal and treatment effects were compared statistically.  While there was a fair amount of variability between sites at different location around the state there was no statistical difference in yield at any of the sites over the rates of N application studied.  This strongly suggests that Utah growers are able to reduce N fertilizer application much more than the traditional 50 unit per acre credit, or perhaps even eliminate it all together.